Recently, the performance and functionality of digital cameras and digital movie cameras that use some solid-state image sensor such as a CCD and a CMOS (which will be sometimes simply referred to herein as an “image sensor”) have been enhanced to an astonishing degree. In particular, the size of a pixel structure for use in an image sensor has been further reduced these days thanks to rapid development of semiconductor device processing technologies, thus getting an even greater number of pixels and drivers integrated together in an image sensor. As a result, the resolution of an image sensor has lately increased rapidly from one million pixels to ten million or more pixels in a matter of few years. On top of that, the quality of an image captured has also been improved significantly as well. As for display devices, on the other hand, LCD and plasma displays with a reduced depth now provide high-resolution and high-contrast images, thus realizing high performance without taking up too much space. And such video quality improvement trends are now spreading from 2D images to 3D images. In fact, 3D display devices that achieve high image quality although they require the viewer to wear a pair of polarization glasses have been developed just recently and put on the market one after another.
As for the 3D image capturing technology, a typical 3D image capture device with a simple arrangement uses an image capturing system with two cameras to capture a right-eye image and a left-eye image. According to the so-called “two-lens image capturing” technique, however, two cameras need to be used, thus increasing not only the overall size of the image capture device but also the manufacturing cost as well. To overcome such a problem, methods for capturing multiple images with parallax by using a single camera have been researched and developed. For example, Patent Document No. 1 discloses a scheme that uses two polarizers, of which the transmission axes cross each other at right angles, and a rotating polarization filter.
FIG. 10 is a schematic representation illustrating an arrangement for an image capturing system that adopts such a scheme. This image capturing system includes a 0-degree-polarization polarizer 11, a 90-degree-polarization polarizer 12, a reflective mirror 13, a half mirror 14, a circular polarization filter 15, a driver 16 that rotates the circular polarization filter 15, an optical lens 3, and an image capture device 9 for capturing the image that has been produced by the optical lens. In this arrangement, the half mirror 14 reflects the light that has been transmitted through the polarizer 11 and then reflected from the reflective mirror 13 but transmits the light that has been transmitted through the polarizer 12. With such an arrangement, the light rays that have been transmitted through the two polarizers 11 and 12, which are arranged at two different positions, pass through the half mirror 14, the circular polarization filter 15 and the optical lens 3 and then enter the image capture device 9, where an image is captured. The image capturing principle of this scheme is that two images with parallax are captured by rotating the circular polarization filter 15 so that the light rays that have entered the two polarizers 11 and 12 are imaged at mutually different times.
According to such a scheme, however, images at mutually different positions are captured time-sequentially by rotating the circular polarization filter 15, and therefore, those images with parallax cannot be captured at the same time, which is a problem. In addition, the durability of such a system is also a question mark because the system uses mechanical driving. On top of that, since all of the incoming light is received by the polarizers and the polarization filter, the quantity of the light received eventually by the image capture device 9 decreases by as much as 50%, which is non-negligible, either.
To overcome these problems, Patent Document No. 2 discloses a scheme for capturing two images with parallax without using such mechanical driving. An image capture device that adopts such a scheme gets the two incoming light rays, which have come from two different directions, condensed by a reflective mirror, and then received by an image capture device in which two different kinds of polarization filters are arranged alternately, thereby capturing two images with parallax without using a mechanical driving section.
FIG. 11 is a schematic representation illustrating an arrangement for an image capturing system that adopts such a scheme. This image capturing system includes two polarizers 11 and 12, of which the transmission axes are arranged to cross each other at right angles, reflective mirrors 13, an optical lens 3, and an image capture device 1. On its imaging area, the image capture device 1 has a number of pixels 10 and polarization filters 17 and 18, each of which is provided one to one for an associated one of the pixels 10. Those polarization filters 17 and 18 are arranged alternately over all of those pixels. In this case, the transmission axis directions of the polarization filters 17 and 18 agree with those of the polarizers 11 and 12, respectively.
With such an arrangement, the incoming light rays are transmitted through the polarizers 11 and 12, reflected from the reflective mirrors 13, passed through the optical lens 3 and then incident on the imaging area of the image capture device 1. Those light rays to be transmitted through the polarizers 11 and 12, respectively, and then incident on the image capture device 1 are transmitted through the polarization filters 17 and 18 and then photoelectrically converted by the pixels that face those polarization filters 17 and 18. If the images to be produced by those light rays that have been transmitted through the polarizers 11 and 12 and then incident on the image capture device 1 are called a “right-eye image” and a “left-eye image”, respectively, then the right-eye image and the left-eye images are generated by a group of pixels that face the polarization filters 17 and a group of pixels that face the polarization filter 18.
As can be seen, according to the scheme disclosed in Patent Document No. 2, two kinds of polarization filters, of which the transmission axes are arranged so as to cross each other at right angles, are arranged alternately over the pixels of the image capture device, instead of using the circular polarization filter disclosed in Patent Document No. 1. As a result, although the resolution decreases to a half compared to the method of Patent Document No. 1, a right-eye image and a left-eye image with parallax can be obtained at the same time by using a single image capture device.
According to such a technique, however, the incoming light has its quantity decreased considerably when being transmitted through the polarizers and the polarization filters, and therefore, the quantity of the light received by the image capture device decreases as significantly as in Patent Document No. 1.
As another approach to the problem that the image capture device comes to receive a decreased quantity of light, Patent Document No. 3 discloses a technique for mechanically changing the modes of operation from the mode of capturing multiple images that have parallax into the mode of capturing a normal image, and vice versa. FIG. 12 schematically illustrates an arrangement for an image capturing system that uses such a technique. The image capture device shown in FIG. 12 includes a light transmitting member 19 that has two polarized light transmitting portions 20 and 21 and that transmits the light that has come from an optical lens 3 only through those transmitting portions, a light receiving member optical filter tray 22 in which particular component transmitting filters 23 that split the light that has come from the polarized light transmitting portions 20 and 21 and color filters 24 are arranged as a set, and a filter driving section 25 that removes the light transmitting member 19 and the particular component transmitting filters 23 from the optical path and inserts the color filters 24 onto the optical path instead, and vice versa.
According to this technique, by running the filter driving section 25, the light transmitting member 19 and the particular component transmitting filters 23 are used to capture two images with parallax, while the color filters 24 are used to capture a normal image. However, the two images with parallax are shot in basically the same way as in Patent Document No. 2, and therefore, the incoming light can be used much less efficiently than in a normal image capturing session. When a normal color image is shot, on the other hand, the light transmitting member 19 is removed from the optical path and the color filters 24 are inserted instead of the particular component transmitting filters 23. As a result, a color image can be generated with the incoming light used highly efficiently.